1999 yamaha v max 200

my motor will start and idol perfect. when I give it a lot of throttle it will start to take off just for a split second and fall on its face or die. I have replaced the filter. cleaned the filter in the vapor tank,and cleaned the fuel tanks and gave it fresh gas. I had took it to a dealer and they supposable cleaned the 02 sensor, put new plugs in and still have same problem . I had the boat on the water yesterday and was trying to get it to run it did take off one time but when I slowed back down it went back to not running right again. Any ideas? thanks tom.